In 1981, R. Edgar Hope-Simpson proposed that a 'seasonal stimulus' intimately associated with solar radiation explained the remarkable seasonality of epidemic influenza. Solar radiation triggers robust seasonal vitamin D production in the skin; vitamin D deficiency is common in the winter, and activated vitamin D, 1,25(OH)2D, a steroid hormone, has profound effects on human immunity. 1,25(OH)2D acts as an immune system modulator, preventing excessive expression of inflammatory cytokines and increasing the 'oxidative burst' potential of macrophages. Perhaps most importantly, it dramatically stimulates the expression of potent anti-microbial peptides, which exist in neutrophils, monocytes, natural killer cells, and in epithelial cells lining the respiratory tract where they play a major role in protecting the lung from infection. Volunteers inoculated with live attenuated influenza virus are more likely to develop fever and serological evidence of an immune response in the winter. Vitamin D deficiency predisposes children to respiratory infections. Ultraviolet radiation (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as does cod liver oil (which contains vitamin D). An interventional study showed that vitamin D reduces the incidence of respiratory infections in children. We conclude that vitamin D, or lack of it, may be Hope-Simpson's 'seasonal stimulus'.

Scand J Caring Sci; 2012; 26; 12–19 
 A community‐based exercise programme to improve functional ability in people with Alzheimer’s disease: a randomized controlled trial Rationale:  Dementia is a common neurodegenerative condition in older age associated with functional decline across multiple domains. This decline impacts not only on the person with dementia, but also on their informal carers and health and aged care systems. With the number of people with dementia rapidly increasing and few effective treatments, there is now a critical need for interventions to improve functional ability in those with the condition. Aims and objective:  This study assesses the effectiveness of a community‐based home exercise programme in improving cognitive and physical function and independence in activities of daily living (ADL) in people with Alzheimer’s disease, the most common form of dementia. Methods:  In a 4‐month randomized controlled trial, 40 community‐dwelling patients diagnosed with Alzheimer’s disease and their informal carers were randomly allocated to either the treatment (exercise plus usual treatment) or control (usual treatment) group. The exercise programme consisted of daily exercises and walking under the supervision of their carer. Patients were assessed at baseline and 4‐months follow‐up by a blinded assessor on primary outcome measures of cognitive and physical function and ADL using standardized assessment scales. Results:  Sixteen men and 24 women diagnosed with Alzheimer’s disease participated in the study. They had a mean age of 74.1 years (range 51–89) and a mean Mini Mental State Examination score of 22.0 (range 10–28), indicating mild to moderate dementia. At 4‐months follow‐up, patients who exercised, compared with controls, had improved cognition (increased Mini Mental State Examination scores by 2.6 points, p < 0.001), better mobility (2.9 seconds faster on Timed Up and Go, p = 0.004) and increased Instrumental Activities of Daily Living scores by 1.6 (p = 0.007). Conclusion:  This study suggests that participation in a community‐based exercise programme can improve cognitive and physical function and independence in ADL in people with Alzheimer’s disease.

Vitamin D may improve athletic performance in vitamin D-deficient athletes. Peak athletic performance may occur when 25(OH)D levels approach those obtained by natural, full-body, summer sun exposure, which is at least 50 ng x mL(-1). Such 25(OH)D levels may also protect the athlete from several acute and chronic medical conditions.

No abstract

The epidemiology of influenza swarms with incongruities, incongruities exhaustively detailed by the late British epidemiologist, Edgar Hope-Simpson. He was the first to propose a parsimonious theory explaining why influenza is, as Gregg said, "seemingly unmindful of traditional infectious disease behavioral patterns." Recent discoveries indicate vitamin D upregulates the endogenous antibiotics of innate immunity and suggest that the incongruities explored by Hope-Simpson may be secondary to the epidemiology of vitamin D deficiency. We identify -and attempt to explainnine influenza conundrums: (1) Why is influenza both seasonal and ubiquitous and where is the virus between epidemics? (2) Why are the epidemics so explosive? (3) Why do they end so abruptly? (4) What explains the frequent coincidental timing of epidemics in countries of similar latitude? (5) Why is the serial interval obscure? (6) Why is the secondary attack rate so low? (7) Why did epidemics in previous ages spread so rapidly, despite the lack of modern transport? (8) Why does experimental inoculation of seronegative humans fail to cause illness in all the volunteers? (9) Why has influenza mortality of the aged not declined as their vaccination rates increased? We review recent discoveries about vitamin D's effects on innate immunity, human studies attempting sick-to-well transmission, naturalistic reports of human transmission, studies of serial interval, secondary attack rates, and relevant animal studies. We hypothesize that two factors explain the nine conundrums: vitamin D's seasonal and population effects on innate immunity, and the presence of a subpopulation of "good infectors." If true, our revision of Edgar Hope-Simpson's theory has profound implications for the prevention of influenza.